When Leena V., 21, moved from South Africa and started college in California, she was overwhelmed by stress. There was the culture shock, which led to social anxiety, then loneliness and doubt. After six months in her new city, she felt stuck. "It seemed as if everyone else was happy and fitting in, and I wanted that for myself," she says. She'd seen a therapist as a teen but didn't find it helpful, and the idea of trying again felt daunting. Yet she was intrigued by BetterHelp, a start-up that offered a different kind of counseling—via online messaging. After being matched with a therapist, Leena started tapping out her worries on her laptop and phone, then waiting for a response (which usually came within 24 hours). "It felt like writing an email to a brilliant friend, yet there was also that professionalism," she says.

Companies like BetterHelp and Talkspace are Uber-fying psychotherapy. They connect subscribers with licensed mental-health professionals who have at least a master's degree as well as clinical experience. Each therapist has favorite methods, so users may be asked to talk about their dreams, childhood, behavior patterns, moods or goals. But unlike a traditional session, conversations don't always take place in real time.

The delayed response can be a bonus. "In face-to-face therapy, some people talk to fill the time," says Nicole Amesbury, head of clinical development and a licensed mental health counselor with Talkspace. Online clients respond at their leisure, and Amesbury says she has more time to formulate her response. She still tries to accommodate clients who need a back-and-forth: In the evening when one client is tempted to binge-text a manipulative boyfriend, Amesbury encourages the client to message her instead. (Sessions aren't typically covered by insurance, but at $12 to $49 per week, they're cheaper than many co-pays.) Amesbury admits that connecting online is different—she can't express empathy by just nodding her head or looking into a patient's eyes. But she says that through writing, "a deep and personal connection can be formed."

Users find that having a therapist in their pocket means they can easily fit a session into their life. One of Amesbury's clients uses her daily bus commute to write about her anger—more productive than, say, fuming in her seat.

And texting may actually help patients open up. One recent study, from The New School for Social Research, found that people give more frank answers to sensitive questions via text than phone interviews—likely because they don't have to answer as immediately. "People speak more freely about pain and struggle than in my face-to-face practice," says Ingrid Middleton, a BetterHelp-affiliated licensed clinical social worker in Honolulu. "In traditional therapy, it can take five sessions before they tell me their problem."

Online clients might start feeling better as soon as they hit SEND. Research has shown that people who engage in deep and meaningful writing (i.e., journaling) report increased well-being and reduced anxiety. While the writing in these studies was done on paper, "one might hypothesize that the effects of text therapy would be similar," says Katherine M. Krpan, Ph.D., who has studied expressive writing and depression. She says the key is to explore deep feelings while writing (or typing) for a minimum of 20 minutes on at least three consecutive days.

Mental-health experts say that mobile therapy is promising but so far unproven. Lynn Bufka, Ph.D., associate executive director at the American Psychological Association, says that while she's seen evidence supporting video-based therapy, the text-based kind hasn't been studied as thoroughly. What's more, therapists are trained to use their senses to assess clients. Text or email doesn't give them a complete picture of your mental health, says Marlene Maheu, Ph.D., a licensed psychologist and executive director of the TeleMental Health Institute.

Text therapy may not be a good fit for those who crave therapy's human contact (though it can be used supplementally). And neither Talkspace nor BetterHelp is intended for people with a mental illness like bipolar disorder or who are in crisis or want to try antidepressants. (Counselors are trained to recognize when a client needs a referral to a specialist or the ER.) As in real life, it's important to find a good match; if you're not happy with your online therapist, you can switch.

Nearly two years since Leena "met" her therapist, she's adjusted to her new life. At first, she was texting every day, then twice a week. Now it's down to once. Still, she says, "I like knowing I can message her anytime something comes up."